Shock strut pressure is measured during maintenance of landing gear and other pressure vessels to ensure proper performance. The physical geometry of these pressure vessels (such as landing gear shock absorbers) determine (along with fluid and gas volumes) the behaviour and performance of the vessel. Measuring the pressure of the gas within the shock absorber is a critical task that must be performed regularly to ensure safe operation of the aircraft. This is presently performed by attaching a gauge to the external port of the charging valve, then opening the valve. This action is suboptimal because it requires a manual operation to connect and read the system, and because it involves the opening and closing of the valve (with the attendant loss of a small amount of fluid or gas).
In order to reduce the amount of required maintenance, an automatic means of measuring the pressure of fluid within the shock strut is desired. Conventional approaches to this problem would involve the mounting of a pressure transducer either directly into the body of the shock strut, or the fitting of a manifold to the existing port to allow both a pressure measurement and a facility to charge (alter the quantity of fluid and gas). Both of these solutions present problems when they are applied to existing shock strut designs. Fitting a transducer into the body of the shock strut involves drilling a hole in the structure of the strut—which is generally not acceptable from a strength or fatigue perspective. Adding a manifold to the shock strut changes the amount of internal working volume, which changes the energy absorbing properties of the landing gear—which is not desirable.
Many landing gears have a poppet charging valve conforming to MS28889-2/MIL-PRF-6164F. This valve allows the introduction or removal of fluid and gas from the pressure vessel. The present invention modifies this valve to include a pressure-sensing means and electrical contact means such that measurements may be made of the working fluid without interfering with the normal operation of the valve or significantly altering the volume within the pressure vessel.
This modified valve can be retrofitted to any landing gear to allow pressure measurements to be made without altering the landing gear. A change in military standards from MS28889-2 to the newer performance based specification—MIL-PRF-6164F allows the certification of a modified valve to act as a replacement for existing valves.